Most collectors are interested in collecting "types," but advanced collectors often see significant differences between coins of the same "type" that they then distinguish as "varieties." The difference between "type"and "variety" is not a matter of fact, it is a matter of choice and opinion, and untimately, personal definition. Here is a case study of an extremely common "type" of Constantine.
The basic type is determined by the legend and design. Obviously, different mintmarks are enough to regard coins as signficantly different "types," but this page omits consideration of mintmarks.
The basic type with legendSOLI INVICTO COMITI
and design
Sol standing left, naked except for a cloak, raising his right hand (in blessing?) and holding a globe in his left hand
[This page is ignoring mintmarks in spite of the fact they are very important to collectors.]
Does the orientation of Sol's lower body make this significantly different? On the above coin the front foot faces left (Sol's right) and on this one the lower body leans to our right. This difference is pretty small. For me it is not significant.
Sol has a whip on a globe instead of a globe. The cape is unusually dramatic. It is significantly different--at least a "variety" and maybe even a different "type". In either case, it is worth a large premium.
This one adds a captive to the lower left. That makes it signifiicantly different. I hesitate to call it a new type, but it is at least a significant variety.
The square cross in the left field is a control mark, but, because of its Christian connection and the fact Constantine was the first Christian emperor, the cross is so important that it makes a very significant variety. It is worth five or ten times as much as the type without the cross. It is the first Roman AE type (variety?) with a Christian connection.
This one has a field mark much like the cross above, but other examples show it is an "X" not quite tilted correctly. This one is, in my opinion, not a Christian cross. It is just the basic type with field marks, one of which is an "X" which is, on this die, engraved poorly and tilted a lot like a cross. It has no premium.
This one qualifies as a new type (or at least an important variety) because Sol holds Victory in place of the globe. The design is different. For me, that is enough to be called a new type.
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